The present invention relates to a heat-sensitive lithographic printing plate precursor which requires no development-processing and can ensure a long press life and high stain resistance. More specifically, the present invention relates to a lithographic printing plate precursor which enables recording of images by scanning exposure to infrared laser beams based on digital signals and, after the images are recorded therein, can be mounted in a printing machine (i.e., a printing press) without undergoing development-processing and can then be subjected to printing operations.
Various methods have been proposed concerning a lithographic printing plate precursor of the kind which enables image formation by heat and can be mounted in a printing machine without development-processing after the image formation. One promising method among them is a method of utilizing an ablation phenomenon, specifically which comprises exposing a printing plate precursor containing a compound capable of converting light to heat by means of a high-output solid-state laser, e.g., a semiconductor laser or a YAG laser, to make the exposed area evolve heat by the compound capable of converting light to heat, thereby causing decomposition and evaporation, namely ablation, in the exposed area.
In other words, a water-receptive layer is provided on a substrate having an oleophilic ink-receptive layer and the water-receptive layer is removed by ablation.
In WO94/18005 is disclosed the printing plate made by providing a cross-linked water-receptive layer on an oleophilic laser beam absorbing layer and subjecting the water-receptive layer to ablation-processing. This water-receptive layer comprises polyvinyl alcohol cross-linked with hydrolysis products of tetraethoxysilane and titanium dioxide grains, and thereby achieves an improvement in strength of the water-receptive layer. Although such a technique enables an increase in impression capacity, it fails in ensuring sufficient stain resistance because the polyvinyl alcohol, which contains hydrocarbon groups and is not so high in water receptivity, comprises 48 weight % of the water-receptive layer. Therefore, further improvement is required for such a water-receptive layer.
In WO98/40212, WO99/19143 and WO99/19144 were disclosed the lithographic printing plate precursors which each comprise on an ink-receptive layer-coated substrate a water-receptive layer containing as a main component a colloid, such as silica, cross-linked with a cross-linking agent, such as aminopropyltriethoxysilane, and can be mounted in a printing machine without development-processing. Such a water-receptive layer achieves the largest possible reduction in content of hydrocarbon groups to ensure an improved stain resistance, and increases its impression capacity by cross-linking the colloid with the cross-linking agent as mentioned above. However, the impression capacity of such a printing plate is several thousand sheets, so it is still insufficient.
The ablation-utilized digital direct processing-free lithographic printing plates as disclosed in the publications described above have great advantages of streamlining processes for printing and reducing waste materials since they enable direct plate-making from block copies without the need for films and the printing plates made can be mounted in a printing machine as they stand and subjected directly to printing operations. However, owing to technical difficulties in making development-processing unnecessary, either of the basic characteristics required for a printing plate, stain resistance or impression capacity, tends to be impaired, so that techniques satisfying both requirements have not yet been developed.
Therefore, an object of the present invention is to solve the aforementioned problems. More specifically, the object of the present invention is to provide a heat-sensitive lithographic printing plate precursor capable of being mounted in a printing machine after exposure and subjected to printing operations as it is without undergoing development-processing, and besides, ensuring both a long press life and high stain resistance.
As a result of our intensive studies, it has been found that the object mentioned above can be attained by developing a specially formulated coating solution for an excellent water-receptive layer, thereby achieving the present invention.
Specifically, embodiments and preferred embodiments of the present invention are described below.
1. A heat-sensitive lithographic printing plate precursor having on a support (1) an ink-receptive layer comprising an oleophilic organic high molecular compound and (2) a water-receptive layer easily allowing removal by a fountain solution or a printing ink when heated, which are arranged in this order: with the water-receptive layer being a layer formed using a coating solution comprising a solvent capable of dissolving the organic high molecular compound of the ink-receptive layer in a proportion of 1 to 40 weight % of the total solvents in the coating solution.
2. The heat-sensitive lithographic printing plate precursor as described in Embodiment 1, wherein the water-receptive layer comprises a hydrophilic resin and a colloid of oxide or hydroxide of at least one element selected from the group consisting of beryllium, magnesium, aluminum, silicon, titanium, boron, germanium, tin, zirconium, iron, vanadium, antimony and transition metals.
3. The heat-sensitive lithographic printing plate precursor as described in Embodiment 2, wherein the hydrophilic resin is contained in a proportion of 0.1 to 30 weight % to the total solid components in the water-receptive layer.
4. The heat-sensitive lithographic printing plate precursor as described in Embodiment 2, wherein the hydrophilic resin is a hydroxyalkyl acrylate homo- or copolymer or a hydroxyalkyl methacrylate homo- or copolymer.